1. Field of the Invention
The invention relates in general to a display system and associated control method, and more particularly to a display system capable of detecting hot-plugging to a host via a DisplayPort interface when versions of DisplayPort standards adopted by the host and a display are different.
2. Description of the Related Art
An early-stage conventional display receives an analog Video Graphic Array (VGA) signal to display images, and the VGA signal is transmitted via a D-sub video port.
Accompanied with the prevalence of digital image data, video interfaces for transmitting digital data have been launched one after another. For example, the Digital Visual Interface (DVI) is announced in 1999, and is mainly targeted at replacing the prior VGA specification used for analog signals in the information technology (IT) industry. For another example, the High Definition Multimedia Interface (HDMI) is announced in 2002, and is mainly targeted at replacing the prior analog AV terminals and S terminals in the consumer electronics (CE) industry.
To enable a display to receive analog or digital image data of different specifications, different video interfaces are provided in the display. FIG. 1 shows a functional block diagram of a display system provided with various video interfaces. A display system 10 comprises a display controller 101, a D-sub engine 103, a DVI engine 105, an HDMI engine 107, a D-sub port 109, a DVI port 111, and an HDMI port 113.
Supposing analog image data outputted from a host (not shown) is to be displayed by the display system 10, and the analog image data is outputted by a D-sub port of the host, connectors (not shown) complying with D-sub interface are respectively connected to the D-sub port of the host (not shown) and the D-sub port 109 of the display system 10. Analog VGA signals outputted from the host are then transmitted to the D-sub engine 103 to generate image signals to the display controller 101 to display images. Similarly, supposing digital image data outputted from a host is to be displayed by the display system 10, and the digital image data is outputted by a DVI port of the host, connectors (not shown) complying with a DVI interface are respectively connected to the DVI port of the host (not shown) and the DVI port 111 of the display system 10. The digital image data outputted from the host is then transmitted to the DVI engine 105 to generate images signals to the display controller 101 to display images. Similarly, supposing digital image data outputted from a host is to be displayed by the display system 10, and the digital image data is outputted by an HDMI port of the host (not shown), connectors (not shown) complying with an HDMI interface are respectively connected to the HDMI port of the host (not shown) and the HDMI port 113 of the display system 10. The digital image data outputted from the host is then transmitted to the HDMI engine 107 to generate images signals to the display controller 101 to display images.
It is observed from the above that, more and more different video interfaces are necessarily provided in a display to accommodate the growing types of video interfaces, such that not only an overall cost is increased but also usage complications are incurred.
To solve the abovementioned complications, the Video Electronics Standards Association (VESA) proposed a new video interface that can be applied in both the IT and CE industries—the new video interface is the DisplayPort standard for replacing the DVI and HDMI standards. One distinct feature of the DisplayPort interface is that the DisplayPort standard is a royalty-free open source, so that all companies can join the VESA for free and participate in modifying and defining the DisplayPort specifications.
FIG. 2 shows a schematic diagram of a signal channel between a host 21 and a display 23 in a DisplayPort interface. Digital image data is transmitted to a display port (DP) 235 and processed by a DP engine (not shown) in the display 23 to generate image signals that are then displayed on the display 23.
In the DisplayPort specifications, a signal channel comprises a main link and an auxiliary channel. The main link handles transmission of image data and is a high-speed one-directional output. The main link comprises four data pairs, each of which comprising two lanes and providing a bandwidth of 2.7 Gbps, so that the four data pairs provide a bandwidth up to 10.8 Gpbs. The auxiliary channel comprises an auxiliary signal pair, which handles information in addition to image data, for example, including status information, control commands, and audio frequencies. The auxiliary channel provides a low-speed bi-directional communication channel for communications between the host 21 and the display 23 before the main link starts to transmit image data. Signals in the main link and the auxiliary channel are differential signals. Further, in the DisplayPort standard, a signal detection end is for outputting a signal detection methodology (SDM) that is mainly for detecting hot-plugging between the host 21 and the display 23 in the DisplayPort version 1.0.
In the DisplayPort version 1.0, the display 23 first detects a level of the SDM to identify whether the display 23 is hot-plugged to the host 21. When it is detected that the display 23 is hot-plugged to the host 21, the host 21 sends a communication signal using an auxiliary signal pair in the auxiliary channel to the display 23 to communicate between the host 21 and the display 23. When the communication between the host 21 and the display 23 is established, the host 21 is allowed to transmit image data to the display 23 via the main link.
However, as stated, DisplayPort is a royalty-free open standard, and all companies can join the VESA for free and participate in modifying and defining the DisplayPort specifications, so that different version of DisplayPort have different definitions for the SDM. In DisplayPort version 1.0, the SDM is used for hot-plug detection between a host 21 and a display 23; yet, in DisplayPort version 1.1 or 1.1a, the SDM serves other functions. Therefore, once the DisplayPort interface standard (e.g., version 1.0) used by the host 21 is different from the DisplayPort interface standard (e.g., version 1.1 or 1.1a) used by the display 23, the display 23 cannot learn whether the display 23 is hot-plugged to the host 21 via the SDM.